Photochemistry of the Hydrogen Selenide-Sulfur Dioxide Complex: Formation of Selenosulfurous Acid and the Dehydrogenated Polyinterchalcogen Compounds.

Polyinterchalcogen compounds consisting of the O, S, and Se atoms are barely known. Herein, we report the synthesis of three O2SSe isomers from photoreaction between hydrogen selenide (H2Se) and sulfur dioxide (SO2) via the intermediacy of selenosulfurous acid (HSeS(O)OH). Specifically, photoexcitation of the chalcogen-bonded (Se•••S) molecular complex between H2Se and SO2 at 310 nm in an Ar-matrix at 10 K yields HSeS(O)OH as an elusive heavy analogue of sulfurous acid (H2SO3). Subsequent photolysis of the matrix-isolated HSeS(O)OH at 254 nm results in dehydration (→ H2O + OSSe) and also dehydrogenation (→ H2 + cis/trans-OSSeO) reactions. Further photoexcitation of cis/trans-OSSeO causes rearrangement to cyc-OS(= O)Se alongside dissociation to Se•••SO2. Characterization of HSeS(O)OH and the O2SSe isomers with matrix-isolation IR and UV-vis spectroscopy is supported by 18O-isotope labeling experiments and high-level quantum chemical calculations. This work advances the fundamental knowledge on chalcogen chemistry, and it also helps in understanding the atmospheric photochemistry of H2Se in the global selenium cycle.